CN116569358A - Positive electrode active material and lithium ion secondary battery - Google Patents
Positive electrode active material and lithium ion secondary battery Download PDFInfo
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- CN116569358A CN116569358A CN202180079355.2A CN202180079355A CN116569358A CN 116569358 A CN116569358 A CN 116569358A CN 202180079355 A CN202180079355 A CN 202180079355A CN 116569358 A CN116569358 A CN 116569358A
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- positive electrode
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 105
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 63
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 58
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
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- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M2300/0065—Solid electrolytes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M2300/0068—Solid electrolytes inorganic
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- H—ELECTRICITY
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- H01M2300/0068—Solid electrolytes inorganic
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a positive electrode active material capable of greatly improving cycle characteristics when assembled in a lithium ion secondary battery. The positive electrode active material comprises a lithium composite oxide having a layered rock salt structure and containing Li, ni, co and Mn, and further comprises a material selected from Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 At least 1 additive of (a) in the composition.
Description
Technical Field
The present invention relates to a positive electrode active material for a lithium ion secondary battery and a lithium ion secondary battery.
Background
As a positive electrode active material layer for a lithium ion secondary battery, a powder-dispersed positive electrode is known, which is obtained by kneading and molding a powder of a lithium composite oxide (typically, a lithium transition metal oxide) with an additive such as a binder or a conductive agent. Since the powder-dispersed positive electrode contains a binder which does not contribute to the capacity in a large amount (for example, about 10% by weight), the packing density of the lithium composite oxide as the positive electrode active material is reduced. Therefore, there is a great room for improvement in the capacity and charge/discharge efficiency of the powder-dispersed positive electrode. Then, an attempt was made to: it is desired to improve capacity and charge/discharge efficiency by constituting the positive electrode or positive electrode active material layer with a lithium composite oxide sintered plate. In this case, since the positive electrode or the positive electrode active material layer does not contain a binder, the packing density of the lithium composite oxide increases, and thus a high capacity and a good charge/discharge efficiency can be expected.
In addition, in lithium ion secondary batteries, a liquid electrolyte (electrolyte solution) using a flammable organic solvent as a diluent solvent has been conventionally used as a medium for moving ions. In a battery using such an electrolyte, problems such as leakage of the electrolyte, ignition, and explosion may occur. In order to eliminate these problems and to ensure intrinsic safety, all-solid batteries have been developed which use a solid electrolyte instead of a liquid electrolyte and in which the other elements are all composed of a solid. Since the electrolyte of the all-solid battery is solid, there is no concern of ignition, no leakage of liquid, and no problem of deterioration of battery performance due to corrosion.
Proposed to use a sintered electrode and a solid electrolyteAll-solid batteries of (a) are provided. For example, patent document 1 (WO 2019/093222 A1) discloses an all-solid lithium battery including: an oriented positive electrode plate which is a lithium composite oxide sintered plate having a void ratio of 10 to 50%; a negative electrode plate containing Ti and capable of supplying lithium ions at 0.4V (Li/Li + ) The above insertion and detachment are carried out; and a solid electrolyte having a melting point lower than the melting point or decomposition temperature of the oriented positive or negative electrode plate. In this document, li is disclosed as such a solid electrolyte having a low melting point 3 OCl、xLiOH·yLi 2 SO 4 (wherein x+y= 1,0.6.ltoreq.x.ltoreq.0.95) (e.g. 3 LiOH. Li 2 SO 4 ) And the like. Such a solid electrolyte can penetrate into the gaps of the electrode plate in the form of a melt, and thus can achieve firm interface contact. As a result, it is possible to achieve significant improvement in battery resistance and rate performance at the time of charge and discharge and significant improvement in battery manufacturing yield. Patent document 2 (WO 2015/151566 A1) discloses an all-solid lithium battery including: an oriented positive plate having a basic composition of Li p (Ni x ，Co y ，Mn z )O 2 (wherein, p is more than or equal to 0.9 and less than or equal to 1.3, x is more than 0 and less than 0.8, y is more than 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 0.7, and x+y+z=1) and has a lamellar rock salt structure; a solid electrolyte layer composed of a Li-La-Zr-O ceramic material and/or a lithium phosphorus oxygen nitrogen (LiPON) ceramic material; and a negative electrode layer.
Prior art literature
Patent literature
Patent document 1: WO2019/093222A1
Patent document 2: WO2015/151566A1
Disclosure of Invention
The inventors of the present invention have found that, in the low-melting solid electrolyte described above, particularly 3 LiOH. Li 2 SO 4 Equivalent LiOH Li 2 SO 4 The solid electrolyte body exhibits high lithium ion conductivity. However, as disclosed in patent document 1 as a comparative example, there is a problem that 3lioh·li is used for the unoriented sintered plate electrode 2 SO 4 Equivalent LiOH Li 2 SO 4 The solid electrolyte constitutes a single cell, and the cycle characteristics are degraded when the cell is operated. Since the unoriented sintered compact has an advantage in that the raw material powder is not easily restricted when the microstructure such as the pore diameter is controlled, the cycle characteristics can be improved by using the unoriented sintered compact. However, the mixture electrode is not limited to the sintered plate electrode, and improvement of cycle characteristics is also desired.
The inventors of the present invention have recently found that a lithium composite oxide for a positive electrode of a lithium ion secondary battery contains a compound selected from the group consisting of Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 At least 1 additive of the above, can greatly improve cycle characteristics.
Accordingly, an object of the present invention is to provide a positive electrode active material that can greatly improve cycle characteristics when assembled in a lithium ion secondary battery.
According to an aspect of the present invention, there is provided a positive electrode active material for a lithium ion secondary battery, wherein the positive electrode active material comprises a lithium composite oxide having a layered rock salt structure containing Li, ni, co, and Mn, and further comprises a metal selected from the group consisting of Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 At least 1 additive of (a) in the composition.
According to another aspect of the present invention, there is provided a lithium ion secondary battery including:
A positive electrode layer containing the positive electrode active material;
a negative electrode layer containing a negative electrode active material; and
LiOH·Li 2 SO 4 a solid electrolyte of LiOH.Li 2 SO 4 A solid electrolyte is interposed between the positive electrode layer and the negative electrode layer.
Drawings
Fig. 1 is an electron micrograph and EPMA map image of a cross section of a positive electrode active material (NCM)/solid electrolyte of the all-solid battery fabricated in example 3. The leftmost image is an electron micrograph (white portion corresponds to NCM and black portion corresponds to solid electrolyte), and from this point to the right, EPMA-mapped images of Mn, co, and Ni are shown in order.
Fig. 2 is an electron micrograph and EPMA map image of a cross section of a positive electrode active material (NCM)/solid electrolyte of the all-solid battery fabricated in example 14. The leftmost image is an electron micrograph (white portion corresponds to NCM and black portion corresponds to solid electrolyte), and from this point to the right, EPMA-mapped images of Mn, co, and Ni are shown in order.
Fig. 3 is an electron micrograph (reflected electron image) of a cross section of the positive electrode plate fabricated in example 8.
Fig. 4 is an electron micrograph (reflected electron image) of a cross section of the positive electrode plate after resin filling of the positive electrode plate manufactured in example 12.
Detailed Description
Positive electrode active material
The positive electrode active material of the present invention is used for a lithium ion secondary battery. The positive electrode active material contains a lithium composite oxide having a layered rock salt structure, which contains Li, ni, co and Mn. And the positive electrode active material further contains a material selected from Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 At least 1 additive of (a) in the composition. By thus making the lithium composite oxide for a lithium ion secondary battery contain a metal selected from Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 At least 1 additive in (a) can greatly improve cycle characteristics (particularly cycle maintenance rate).
As described above, if a non-oriented sintered body electrode is used 3LiOH Li 2 SO 4 Equivalent LiOH Li 2 SO 4 When a single cell is constituted by a solid electrolyte and a battery is operated, there is a problem of a decrease in cycle characteristics, but according to the present invention, the problem is solved smoothly. For example, a lithium ion secondary battery having a higher cycle retention rate than a battery using a lithium composite oxide without addition as a positive electrode, the lithium ion secondary battery comprising: a positive electrode layer containing a material selected from Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 A positive electrode active material of a lithium composite oxide of at least 1 of the above; liOH Li 2 SO 4 Tying a solid electrolyte; and a negative electrode layer. The mechanism is not yet defined and is considered as follows. First, as a main cause of deterioration of cycle characteristics, it is presumed that: (1) During charge and discharge, side reactions occur at the interface between the positive electrode and the solid electrolyte, resulting in degradation of the solid electrolyte; (2) By the expansion and contraction of the lithium composite oxide accompanying charge and discharge, fine cracks are generated at the grain boundaries of the lithium composite oxide. In this regard, in the present invention, for the main reason of the above (1), it is presumed that Li precipitated on at least a part of the surface of the lithium composite oxide 3 BO 3 、Li 3 PO 4 And/or Li 2 SO 4 Inhibit side reactions. In addition, for the main cause of the above (2), it is presumed that Li precipitated in at least a part of the grain boundary 3 BO 3 、Li 3 PO 4 And/or Li 2 SO 4 The stress of expansion and contraction is relaxed. Therefore, the additive is preferably present in a state of being precipitated in at least a part of the grain boundary and the surface of the lithium composite oxide.
The positive electrode active material contains a lithium composite oxide having a layered rock salt structure, which contains Li, ni, co, and Mn. The lithium composite oxide is also called cobalt nickel lithium manganate, abbreviated as NCM. The lamellar rock salt structure refers to: a crystal structure in which lithium layers and transition metal layers other than lithium are alternately laminated with an oxygen layer interposed therebetween (typically, α -NaFeO 2 Form structure, i.e. transition metal and lithium along cubic rock salt form structure [111 ]]A structure in which the axial directions are regularly arranged). Typical NCM has a composition of Li p (Ni x ，Co y ，Mn z )O 2 (wherein 0.9.ltoreq.p.ltoreq.1.3, 0 < x.ltoreq.0.8, 0 < y.ltoreq.1, 0.ltoreq.z.ltoreq.0.7, x+y+z=1, preferably 0.95.ltoreq.p.ltoreq. 1.10,0.1.ltoreq.x.ltoreq.0.7, 0.1.ltoreq.y.ltoreq.0.9, 0.ltoreq.z.ltoreq.0.6, x+y+z=1), for example Li (Ni) 0.5 Co 0.2 Mn 0.3 )O 2 Li (Ni) 0.3 Co 0.6 Mn 0.1 )O 2 . Therefore, the molar ratio of Li/(Ni+Co+Mn) in the positive electrode active material is preferably 0.95 to 1.10, more preferably 0.97 to 1.08, and even more preferably0.98 to 1.05.
As described above, the positive electrode active material of the present invention is used for a lithium ion secondary battery, and in this case, the positive electrode is preferably in the form of a sintered plate obtained by sintering a positive electrode raw material powder. That is, the positive electrode active material is preferably in the form of a sintered plate. In other words, the positive electrode active material preferably has a structure in which a plurality of primary particles having a layered rock salt structure containing Li, ni, co, and Mn are bonded. The sintered plate does not contain an electron conduction auxiliary agent or a binder, and therefore, the energy density of the positive electrode can be increased. The sintered plate may be a dense body or a porous body, and the pores of the porous body may contain a solid electrolyte. However, the positive electrode may be a mixture of a positive electrode active material, an electron conduction auxiliary agent, a lithium ion conductive material, a binder, or the like, which is generally called a mixture electrode, or a mixture of a positive electrode active material, lioh·li 2 SO 4 A mixture of a solid electrolyte, an electron transfer auxiliary agent, and the like is molded to obtain a form (a form of a mixture). In this case, the positive electrode active material may be in the form of powder. Thus, the positive electrode active material may be a powder containing a lithium composite oxide and be selected from Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 A mixed powder of at least 1 powder of the above.
The content of the additive occupied in the positive electrode active material (i.e., the content of the additive relative to the total content of the lithium composite oxide and the additive) is preferably 0.1 to 10 wt%, more preferably 0.5 to 7.0 wt%, even more preferably 1.0 to 6.0 wt% from the viewpoint of improving cycle characteristics, regardless of the form of the positive electrode (sintered plate or mixture). The above-mentioned content of the additive is considered to be hardly changed in the additive loading amount at the time of producing the positive electrode active material and the additive content in the final positive electrode active material. This can be deduced, for example, from the fact that there is little change in weight in the case of Thermogravimetry (TG) of the additive monomer.
In the case where the positive electrode active material is in the form of a sintered plate, the sintered plate has an orientation degree I [003] /I [104] From 1.2 to 3.6, preferably from 1.2 to 3.5, more preferablySelected from 1.2 to 3.0, more preferably 1.2 to 2.6, the degree of orientation I [003] /I [104] The definition is as follows: diffraction intensity I from (003) plane in XRD curve measured by X-ray diffraction (XRD) [003] Relative to the diffraction intensity I originating from the (104) plane [104] Is a ratio of (2). Here, the lithium composite oxide having a layered rock salt crystal structure such as NCM has crystal planes (other than the (003) plane, for example, the (101) plane and the (104) plane) which are planes for allowing and removing lithium ions, and the (003) plane which is not plane for allowing and removing lithium ions. In this specification, for convenience, the XRD diffraction intensities of the above (003) plane and (104) plane are used as an index for calculating the degree of orientation. If the sintered plate has an orientation degree I within the above range [003] /I [104] The value of the degree of orientation I of the non-oriented target NCM powder [003] /I [104] (e.g., 1.4 (Ni: co: mn=5:2:3 composition), 2.3 (Ni: co: mn=3:6:1 composition)) are equal or close, and thus can be said to be nearly unoriented (random), i.e., unoriented (or less oriented) in nature. As described above, the unoriented sintered compact has an advantage that it is not easily restricted by the raw material powder when the microstructure such as the pore diameter is controlled, and therefore, the raw material powder preferable for controlling the microstructure (for example, the pore diameter) of the sintered compact is easily selected, and improvement of the cycle characteristics is more easily achieved.
When the positive electrode active material is in the form of a sintered plate, the porosity of the sintered plate is preferably 20 to 40%, more preferably 20 to 38%, even more preferably 20 to 36%, and particularly preferably 20 to 33%. If the amount is within the above range, in the case of manufacturing a battery, the solid electrolyte can be sufficiently filled in the pores, and since the proportion of the positive electrode active material in the positive electrode increases, a high energy density as a battery can be achieved.
In the present specification, "porosity" is: volume ratio of pores in the sintered plate. The porosity can be measured by image analysis of a cross-sectional SEM image of the sintered plate. For example, the sintered plate may be subjected to resin filling, cross-sectional polishing by ion milling, and then the polished cross-section may be observed by SEM (scanning electron microscope), a cross-sectional SEM image (for example, 500 to 1000 times magnification) may be obtained, the obtained SEM image may be analyzed, and the ratio (%) of the area of the portion filled with the resin to the total area of the portion of the electrode active material and the portion filled with the resin (the portion originally being the air hole) may be calculated, thereby calculating the porosity (%) of the sintered plate. If the measurement can be performed with a desired accuracy, the porosity can be measured without embedding the sintered plate with resin. For example, a sintered plate (positive electrode plate taken out from an all-solid secondary battery) having a solid electrolyte filled in the air hole can be subjected to measurement of the porosity in a state of being filled with the solid electrolyte.
When the positive electrode active material is in the form of a sintered plate, the sintered plate preferably has an average pore diameter of 3.5 μm or more, more preferably 3.5 to 15.0 μm, still more preferably 3.5 to 10.0 μm, and particularly preferably 3.5 to 8.0 μm. If the amount is within the above range, the solid electrolyte portion (solid electrolyte portion at a distance away from the interface) which is less likely to be degraded by side reactions between the solid electrolyte and the lithium composite oxide increases. Thus, it is considered that: element diffusion between the solid electrolyte and the lithium composite oxide is suppressed, and degradation of Li ion conductivity due to degradation of the solid electrolyte is alleviated, thereby more effectively improving discharge capacity and cycle characteristics.
In the present specification, "average gas pore diameter" is: average value of diameters of pores contained in the sintered plate of the electrode. The "diameter" mentioned above is typically: the length of a line segment (martin diameter) bisecting the projected area of the air hole. In the present invention, the "average value" is calculated appropriately based on the number. The average gas pore diameter can be measured by image analysis of a cross-sectional SEM image of the sintered plate. For example, the SEM image obtained by the above-described porosimetry may be analyzed, the portion of the electrode active material and the portion filled with the resin (the portion originally being the air hole) in the sintered plate may be cut, and then the maximum martin diameter of each region may be obtained in the region of the portion filled with the resin, and the average value of these may be defined as the average pore diameter of the sintered plate. If the measurement can be performed with a desired accuracy, the average pore size can be measured without resin filling the sintered plate. For example, a sintered plate (positive electrode plate taken out from an all-solid secondary battery) having a solid electrolyte filled in the air hole may be subjected to measurement of the average pore diameter in a state of being filled with the solid electrolyte.
In the case where the positive electrode active material is in the form of a sintered plate, the sintered plate is formed at a thickness of 1 μm 2 The interface length per unit cross-sectional area is preferably 0.45 μm or less, more preferably 0.10 to 0.40 μm, still more preferably 0.10 to 0.35 μm, and particularly preferably 0.10 to 0.30 μm. If the amount is within the above range, the area where side reactions of the lithium composite oxide and the solid electrolyte occur is reduced. Thus, it is considered that: element diffusion between the solid electrolyte and the lithium composite oxide is suppressed, and degradation of Li ion conductivity due to degradation of the solid electrolyte is alleviated, thereby more effectively improving discharge capacity and cycle characteristics.
"every 1 μm" in the present specification 2 The interfacial length "per unit sectional area is: every 1 μm of the sintered plate 2 The total length of the interfaces between all pores and active material contained in the unit cross-sectional area. The interface length can be determined by image analysis of a cross-sectional SEM image of the sintered plate. For example, the SEM image obtained by the above-described porosimetry is analyzed, the portion of the electrode active material and the portion filled with the resin (originally the portion of the air hole) in the sintered plate are cut, and then the perimeter of the entire region (i.e., the total length of the interface between the portion of the positive electrode active material and the portion filled with the resin) and the area of the entire region analyzed (i.e., the region including both the portion of the positive electrode active material and the portion filled with the resin) are obtained in the region of the portion filled with the resin. Then, the circumferential length was divided by the area of the entire region analyzed to be 1 μm 2 The interfacial length per unit cross-sectional area is sufficient. If the measurement can be performed with a desired accuracy, the interface length can be measured without embedding the sintered plate with resin. For example, a sintered plate (positive electrode plate taken out from an all-solid secondary battery) having a solid electrolyte filled in the air hole can be subjected to measurement of the interface length in a state of being filled with the solid electrolyte.
The thickness of the positive electrode is preferably 30 to 300 μm, more preferably 50 to 300 μm, even more preferably 80 to 300 μm, from the viewpoint of increasing the energy density of the battery, regardless of the form of the positive electrode (sintered plate or mixture).
Method for manufacturing lithium composite oxide sintered plate
The lithium composite oxide sintered plate according to the preferred embodiment of the present invention can be produced by any method, but is preferably produced by (a) production of an NCM raw material powder, (b) production of an NCM green sheet, and (c) firing of the NCM green sheet.
(a) Preparation of NCM raw material powder
First, NCM raw material powder was prepared. The preferred NCM starting material powder is Li (Ni 0.5 Co 0.2 Mn 0.3 )O 2 Powder or Li (Ni) 0.3 Co 0.6 Mn 0.1 )O 2 And (3) powder. Li (Ni) 0.5 Co 0.2 Mn 0.3 )O 2 The powder can be produced by mixing (Ni) in such a manner that the molar ratio of Li/(Ni+Co+Mn) is 1.00 to 1.30 0.5 Co 0.2 Mn 0.3 )(OH) 2 Powder and Li 2 CO 3 After mixing the powders, the mixture is fired at 700 to 1200 ℃ (preferably 750 to 1000 ℃) for 1 to 24 hours (preferably 2 to 15 hours). In addition, li (Ni 0.3 Co 0.6 Mn 0.1 )O 2 The powder can be preferably produced by mixing (Ni) in such a manner that the molar ratio of Li/(Ni+Co+Mn) is 1.00 to 1.30 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder and Li 2 CO 3 After mixing the powders, the mixture is fired at 700 to 1200 ℃ (preferably 750 to 1000 ℃) for 1 to 24 hours (preferably 2 to 15 hours).
In order to control the microstructure (particularly pores) peculiar to the lithium composite oxide sintered plate of the present embodiment, it is preferable to prepare a slightly larger NCM raw material powder having a volume-based D50 particle diameter of 3 to 20 μm (preferably 5 to 15 μm) and a slightly smaller NCM raw material powder having a volume-based D50 particle diameter of 0.05 to 1 μm (preferably 0.1 to 0.6 μm), and to use a mixed powder obtained by mixing these. The proportion of the slightly larger NCM raw material powder in the above 2-size mixed powder is preferably 50 to 99% by weight, more preferably 70 to 95% by weight. The slightly smaller NCM raw material powder may be produced by pulverizing the slightly larger NCM raw material powder by a known method such as a ball mill.
Li 3 BO 3 、Li 3 PO 4 、Li 2 SO 4 The additive may be added to the NCM raw material powder after firing produced as described above, or may be added to (Ni 0.5 Co 0.2 Mn 0.3 )(OH) 2 Powder, (Ni) 0.3 Co 0.6 Mn 0.1 )(OH) 2 And (c) in the NCM precursor powder before the calcination. In addition, when the mixed powder of 2 kinds of sizes as described above is obtained, an additive may be added to at least any one of the slightly larger NCM raw material powder and the slightly smaller NCM raw material powder.
(b) Manufacture of NCM Green sheet
The NCM raw material powder (preferably the NCM mixed powder described above), a solvent, a binder, a plasticizer, and a dispersant are mixed to prepare a paste. The obtained paste was subjected to viscosity adjustment and then molded into a sheet shape, thereby producing an NCM green sheet.
(c) Manufacture of NCM sintered plate
The NCM green sheet thus produced was cut into a desired size and shape, placed in a firing sagger, and fired. The firing is preferably performed at a temperature rising rate of 50 to 600 ℃/h (preferably 100 to 300 ℃/h) to 800 to 1000 ℃ (preferably 850 to 970 ℃) and for 1 to 24 hours (preferably 2 to 12 hours). Thus, a lithium composite oxide sintered plate (NCM sintered plate) was obtained.
Lithium ion secondary battery
The positive electrode active material of the present invention is used for a lithium ion secondary battery (typically, an all-solid-state battery). Therefore, according to a preferred embodiment of the present invention, there is provided a lithium ion secondary battery comprising: positive electrode layer, negative electrode layer, and LiOH-Li containing the positive electrode active material of the present invention 2 SO 4 And a solid electrolyte is tied. The anode layer contains an anode active material. LiOH Li 2 SO 4 A solid electrolyte interposed between the positive electrode and the negative electrodeBetween the layers and the negative electrode layer. As described above, li is to be added to 3 BO 3 、Li 3 PO 4 And/or Li 2 SO 4 The lithium-ion secondary battery using the lithium composite oxide of (a) for the positive electrode layer can exhibit a higher cycle retention rate than a conventional lithium-ion secondary battery using a lithium composite oxide without an additive for the positive electrode layer.
The positive electrode layer is preferably in the form of a sintered plate obtained by sintering a positive electrode raw material powder. That is, the positive electrode active material is preferably in the form of a sintered plate. The sintered plate does not contain an electron conduction auxiliary agent or a binder, and therefore, the energy density of the positive electrode layer can be increased. The sintered plate may be a dense body or a porous body, and the pores of the porous body may contain a solid electrolyte. However, the positive electrode layer may be a mixture of a positive electrode active material, an electron conduction auxiliary agent, a lithium ion conductive material, a binder, or the like, which is commonly called a mixture electrode, or a mixture of a positive electrode active material, lioh·li 2 SO 4 A mixture of a solid electrolyte, an electron transfer auxiliary agent, and the like is molded to obtain a form (a form of a mixture). That is, the positive electrode layer may contain particles of the positive electrode active material, lioh·li, in the form of a mixture 2 SO 4 Particles of a solid electrolyte and an electron conduction auxiliary agent. Regarding the form of the positive electrode, the density (filling ratio) of the positive electrode active material in the positive electrode in the form of a mixture is preferably 50 to 80% by volume, more preferably 55 to 80% by volume, still more preferably 60 to 80% by volume, and particularly preferably 65 to 75% by volume. If the density is within such a range, the solid electrolyte can be sufficiently filled in the voids in the positive electrode active material, and the proportion of the positive electrode active material in the positive electrode increases, so that a high energy density as a battery can be achieved. The density (filling rate) in the mixture form corresponds to a value obtained by subtracting the proportion of the portion (including the pores) other than the positive electrode active material from 100.
The negative electrode layer (typically, a negative electrode plate) contains a negative electrode active material. As the negative electrode active material, a negative electrode active material commonly used in lithium ion secondary batteries can be used. Examples of such a general negative electrode active material include: a metal or semi-metal such as a carbon material or Li, in, al, sn, sb, bi, si, or an alloy containing any of them. Further, an oxide-based negative electrode active material may be used.
Particularly preferred negative electrode active materials include materials capable of supplying lithium ions at 0.4V (for Li/Li + ) The above material to be inserted and removed preferably contains Ti. The negative electrode active material satisfying the above conditions is preferably an oxide containing at least Ti. Preferable examples of such a negative electrode active material include: lithium titanate Li 4 Ti 5 O 12 (hereinafter sometimes referred to as LTO) and niobium-titanium composite oxide Nb 2 TiO 7 Titanium oxide TiO 2 More preferably LTO and Nb 2 TiO 7 LTO is more preferable. LTO is known to have a spinel-type structure, but other structures may be used in charge and discharge. For example, LTO is charged and discharged with Li 4 Ti 5 O 12 (spinel structure) and Li 7 Ti 5 O 12 The two phases (of rock salt structure) coexist to react. Thus, LTO is not limited to spinel structures.
The negative electrode may be a mixture of a negative electrode active material, an electron conduction auxiliary agent, a lithium ion conductive material, a binder, or the like, which is commonly called a mixture electrode, or a negative electrode active material, liOH-Li 2 SO 4 A solid electrolyte, an electron conduction auxiliary agent, and the like. That is, the negative electrode may contain particles of the negative electrode active material, lioh·li, in the form of a mixture 2 SO 4 Particles of a solid electrolyte and an electron conduction auxiliary agent. However, the negative electrode is preferably in the form of a sintered plate obtained by sintering a negative electrode raw material powder. That is, the negative electrode or the negative electrode active material is preferably in the form of a sintered plate. The sintered plate does not contain an electron conduction auxiliary agent or a binder, and therefore, the energy density of the anode can be increased. The sintered plate may be a dense body or a porous body, and the pores of the porous body may contain a solid electrolyte. In the form of a mixture, the particle diameter of the negative electrode active material particles is preferably 0.05 to 50. Mu.m, more preferably 0.1 to 30. Mu.m, and still more preferably 0.5 to 20. Mu.m. LiOH Li 2 SO 4 The particle diameter of the solid electrolyte particles is preferably 0.01 to 50. Mu.m, more preferably 0.05 to 30. Mu.m, and still more preferably 0.1 to 20. Mu.m. The electron conductive additive is not particularly limited as long as it is an electron conductive substance generally used for an electrode, and is preferably a carbon material. Preferable examples of the carbon material include: carbon black, graphite, carbon nanotubes, graphene, reduced graphene oxide, and any combination thereof, but the present invention is not limited thereto, and other various carbon materials may be used.
The density (filling ratio) of the negative electrode active material in the negative electrode is preferably 55 to 80% by volume, more preferably 60 to 80% by volume, and even more preferably 65 to 75% by volume, regardless of the form (sintered plate or mixture) of the negative electrode. If the density is within this range, the solid electrolyte can be sufficiently filled in the voids in the anode active material, and the proportion of the anode active material in the anode increases, so that a high energy density as a battery can be achieved. The density (filling rate) in the mixture form corresponds to a value obtained by subtracting the proportion of the portion (including the pores) other than the negative electrode active material from 100.
The thickness of the negative electrode is preferably 40 to 410 μm, more preferably 65 to 410 μm, even more preferably 100 to 410 μm, particularly preferably 107 to 270 μm, from the viewpoint of increasing the energy density of the battery, etc., irrespective of the form of the negative electrode (sintered plate or mixture).
The solid electrolyte is LiOH-Li 2 SO 4 And a solid electrolyte is tied. LiOH Li 2 SO 4 The solid electrolyte is LiOH and Li 2 SO 4 Typical compositions are of the general formula: xlio yLi 2 SO 4 (in the formula, x+y= 1,0.6.ltoreq.x.ltoreq.0.95), and as a representative example, 3 LiOH. Li 2 SO 4 (composition of x=0.75 and y=0.25 in the above formula). Preferably, liOH. Li 2 SO 4 The solid electrolyte contains 3 LiOH-Li identified by X-ray diffraction 2 SO 4 Is a solid electrolyte of (a). The preferred solid electrolyte comprises 3 LiOH. Li 2 SO 4 As the main phase. Authentication by using 032-0598 of ICDD database in X-ray diffraction patternIt was confirmed whether or not 3 LiOH. Li was contained in the solid electrolyte 2 SO 4 . Here, "3 LiOH. Li 2 SO 4 "means that the crystalline structure is regarded as 3 LiOH. Li 2 SO 4 The same material, the crystalline composition does not necessarily need to be 3LiOH Li 2 SO 4 The same applies. That is, as long as it has a molecular structure of 3 LiOH. Li 2 SO 4 Equivalent crystalline structure is sufficient, composition deviates from LiOH: li (Li) 2 SO 4 =3: 1 is also contained in "3 LiOH. Li 2 SO 4 "in". Therefore, even a solid electrolyte containing a dopant such as boron (e.g., 3lioh·li in which boron is solid-dissolved and the X-ray diffraction peak moves to the high-angle side) 2 SO 4 ) So long as the crystalline structure is regarded as 3 LiOH. Li 2 SO 4 The same is 3LiOH Li mentioned in the specification 2 SO 4 . Likewise, the solid electrolyte used in the present invention is also allowed to contain unavoidable impurities.
Thus, liOH. Li 2 SO 4 The solid electrolyte contains 3LiOH Li as a main phase 2 SO 4 In addition, heterogeneous phases may be included. The hetero-phase may contain a plurality of elements selected from Li, O, H, S and B, or may be composed of only a plurality of elements selected from Li, O, H, S and B. Examples of the hetero-phase include LiOH and Li derived from the raw materials 2 SO 4 And/or Li 3 BO 3 Etc. These heterogeneous phases are thought to be responsible for the formation of 3 LiOH. Li 2 SO 4 Since unreacted raw materials remain and do not contribute to lithium ion conduction, li is preferably removed 3 BO 3 The amount of out-of-phase is smaller. However, like Li 3 BO 3 Such a heterogeneous phase containing boron can contribute to an improvement in lithium ion conductivity after a long-term retention at high temperature, and thus can be contained in a desired amount. However, the solid electrolyte may be composed of 3 LiOH. Li in which boron is solid-dissolved 2 SO 4 Is composed of a single phase.
LiOH·Li 2 SO 4 Solid electrolyte (especially 3 LiOH. Li) 2 SO 4 ) Preferably further comprising boron. By making it identified as 3 LiOH. Li 2 SO 4 Further contains boron, and can significantly suppress the decrease in lithium ion conductivity even after the solid electrolyte is maintained at a high temperature for a long period of time. Speculation: boron is introduced into 3 LiOH. Li 2 SO 4 Any of the crystal structure sites of (a) improves the stability of the crystal structure against temperature. The molar ratio (B/S) of boron B to sulfur S contained in the solid electrolyte is preferably more than 0.002 and less than 1.0, more preferably 0.003 or more and 0.9 or less, and still more preferably 0.005 or more and 0.8 or less. If the B/S is within the above range, the retention rate of lithium ion conductivity can be improved. In addition, if the B/S is within the above range, the content of unreacted heterogeneous phase including boron is reduced, and therefore, the absolute value of lithium ion conductivity can be improved.
LiOH·Li 2 SO 4 The solid electrolyte may be a powder compact of a powder obtained by pulverizing a molten and solidified body, and is preferably a molten and solidified body (i.e., a solid obtained by solidifying a molten and solidified body by heating). The method of pulverizing the fused solid is not particularly limited, and a method using a mortar, a ball mill, a jet mill, a roll mill, a cutting mill, a ring mill, or the like can be used, and may be wet or dry.
LiOH·Li 2 SO 4 The solid electrolyte is preferably further filled in the pores of the positive electrode layer and/or the pores of the negative electrode layer, or is (as a component of the mixture) further embedded in the positive electrode layer and/or the negative electrode layer. From the viewpoints of charge/discharge rate characteristics and insulating properties of the solid electrolyte, the thickness of the solid electrolyte layer (excluding the portions of pores entering the positive electrode layer and the negative electrode layer) is preferably 1 to 500 μm, more preferably 3 to 50 μm, and even more preferably 5 to 40 μm.
Manufacturing of lithium ion secondary battery
In the case of using the sintered plate electrode, the lithium ion secondary battery may be manufactured as follows: i) Preparing a positive electrode (with a current collector formed as needed) and a negative electrode (with a current collector formed as needed); ii) the solid electrolyte is sandwiched between the positive electrode and the negative electrode, and the positive electrode, the solid electrolyte and the negative electrode are integrated by applying pressure, heating, or the like. A positive electrode,The solid electrolyte and the negative electrode may be combined by other methods. In this case, as an example of a method of forming a solid electrolyte between a positive electrode and a negative electrode, there is given: a method of placing a solid electrolyte compact or powder on one electrode, a method of applying a paste of solid electrolyte powder on an electrode by screen printing, a method of impinging and solidifying a solid electrolyte powder on an electrode as a substrate by an aerosol deposition method or the like, a method of depositing a solid electrolyte powder on an electrode by an electrophoresis method, and the like. On the other hand, in the case of using a mixture electrode, the production of an all-solid secondary battery can be performed by, for example, placing a positive electrode mixture powder (containing positive electrode active material particles, solid electrolyte particles, and an electron conduction auxiliary agent), a solid electrolyte powder, and a negative electrode mixture powder (containing negative electrode active material particles, solid electrolyte particles, and an electron conduction auxiliary agent) in a pressing mold, and pressurizing them, respectively, to thereby produce an all-solid secondary battery. The various powders may be placed and pressed in this order, and the order of the final positive electrode layer, solid electrolyte layer, and negative electrode layer may be arbitrary. As described above, the positive electrode active material particles may be a powder containing a lithium composite oxide and may be selected from Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 In the form of a mixed powder of at least 1 powder.
Examples
The present invention is further specifically described by the following examples. In the following description, li (Ni 0.5 Co 0.2 Mn 0.3 )O 2 、Li(Ni 0.3 Co 0.6 Mn 0.1 )O 2 The lithium composite oxide having a layered rock salt structure containing Li, ni, co and Mn is abbreviated as "NCM", li 4 Ti 5 O 12 Simply referred to as "LTO".
< examples 1 to 18 >
The examples described below are examples of all-solid secondary batteries in which the positive electrode and the negative electrode are in the form of sintered plates.
First, NCM raw material powders 1 to 22 for producing positive electrode plates were produced as follows. The characteristics of these raw material powders are summarized in tables 1A to 1C.
[ production of NCM raw material powder 1 ]
Commercially available (Ni) was weighed so that the molar ratio of Li/(Ni+Co+Mn) was 1.15 0.5 Co 0.2 Mn 0.3 )(OH) 2 Powder (average particle diameter 9-10 μm) and Li 2 CO 3 After mixing the powders (average particle diameter: 3 μm), they were kept at 750℃for 10 hours to obtain NCM raw material powder 1. The powder had a volume-based D50 particle size of 8. Mu.m.
[ production of NCM raw material powder 2 ]
Adding Li to NCM raw material powder 1 3 BO 3 (relative to NCM raw material powder 1 and Li 3 BO 3 The total amount of (a) was 2.45 wt%, and the NCM raw material powder 2 was obtained by wet grinding with a ball mill, adjusting the volume-based D50 particle diameter to about 0.4 μm, and then drying.
[ production of NCM raw material powder 3 ]
Adding Li to NCM raw material powder 1 3 BO 3 (relative to NCM raw material powder 1 and Li 3 BO 3 The total amount of (2) was 9.2 wt%, and the NCM raw material powder 3 was obtained by wet grinding with a ball mill, adjusting the volume-based D50 particle diameter to about 0.4 μm, and then drying.
[ production of NCM raw material powder 4 ]
The NCM raw material powder 1 was wet-pulverized by a ball mill, and the volume-based D50 particle size was adjusted to about 5.5 μm, followed by drying to obtain NCM raw material powder 4.
[ production of NCM raw material powder 5 ]
Adding Li to NCM raw material powder 1 3 PO 4 (relative to NCM raw material powder 1 and Li 3 PO 4 The total amount of (a) was 1.0 wt%, and the powder was wet-pulverized by a ball mill to adjust the volume-based D50 particle diameter to about 5.5 μm, and then dried to obtain NCM raw material powder 5.
[ production of NCM raw material powder 6 ]
Adding Li to NCM raw material powder 1 3 PO 4 (relative to NCM raw material powder 1Li 3 PO 4 The total amount of (a) was 5.0 wt%, and the powder was wet-pulverized by a ball mill to adjust the volume-based D50 particle diameter to about 5.5 μm, and then dried to obtain NCM raw material powder 6.
[ production of NCM raw material powder 7 ]
Commercially available (Ni) was weighed so that the molar ratio of Li/(Ni+Co+Mn) was 1.15 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder (average particle diameter 7-8 μm) and Li 2 CO 3 After mixing the powders (average particle diameter: 3 μm), they were kept at 850℃for 10 hours to obtain NCM raw material powder 7. The powder had a volume-based D50 particle size of 6.5. Mu.m.
[ production of NCM raw material powder 8 ]
Adding Li to NCM raw material powder 7 3 BO 3 (relative to NCM raw material powder 7 and Li 3 BO 3 The total amount of (a) was 9.2 wt%, and the powder was wet-pulverized by a ball mill to adjust the volume-based D50 particle diameter to about 0.4 μm, and then dried to obtain NCM raw material powder 8.
[ production of NCM raw material powder 9 ]
Adding Li to NCM raw material powder 7 3 BO 3 (relative to NCM raw material powder 7 and Li 3 BO 3 The total amount of (2) was 16.8 wt%, and the NCM raw material powder 9 was obtained by wet grinding with a ball mill, adjusting the volume-based D50 particle diameter to about 0.4 μm, and then drying.
[ production of NCM raw material powder 10 ]
Adding Li to NCM raw material powder 7 3 BO 3 (relative to NCM raw material powder 7 and Li 3 BO 3 The total amount of (a) was 51 wt%, and the NCM raw material powder 10 was obtained by wet grinding with a ball mill, adjusting the volume-based D50 particle diameter to about 0.4 μm, and then drying.
[ production of NCM raw material powder 11 ]
Adding Li to NCM raw material powder 7 2 SO 4 (relative to NCM raw material powder 7 and Li 2 SO 4 In terms of the total amount of (2) and (2) 16.8% by weight, wet-grinding by a ball mill, and adjusting the volume-based D50 particle diameter to about 0.4 μm Drying was performed to obtain NCM raw material powder 11.
[ production of NCM raw material powder 12 ]
Adding Li to NCM raw material powder 7 2 SO 4 (relative to NCM raw material powder 7 and Li 2 SO 4 The total amount of (a) was 51 wt%, and the NCM raw material powder 12 was obtained by wet grinding with a ball mill, adjusting the volume-based D50 particle diameter to about 0.4 μm, and then drying.
[ production of NCM raw material powder 13 ]
The NCM raw material powder 7 was wet-pulverized by a ball mill, and the volume-based D50 particle size was adjusted to about 0.4 μm, followed by drying to obtain NCM raw material powder 13.
[ production of NCM raw material powder 14 ]
The NCM raw material powder 7 was wet-pulverized by a ball mill, and the volume-based D50 particle size was adjusted to about 4.3 μm, followed by drying to obtain NCM raw material powder 14.
[ production of NCM raw material powder 15 ]
Commercially available (Ni) was weighed so that the molar ratio of Li/(Ni+Co+Mn) was 1.15 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder (average particle diameter 7-8 μm) and Li 2 CO 3 The powder (average particle diameter 3 μm) was mixed and then kept at 950℃for 10 hours, and the obtained powder was wet-pulverized by a ball mill, and after adjusting the volume-based D50 particle diameter to about 1.9 μm, the powder was dried to obtain NCM raw material powder 15.
[ production of NCM raw material powder 16 ]
In a range of a molar ratio Li/(Ni+Co+Mn) of 1.15, a commercially available (Ni 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder (average particle diameter 9-10 μm) and Li 2 CO 3 Li is added to the powder (average particle diameter 3 μm) 3 PO 4 Powder (average particle diameter 0.5 μm) (relative to NCM hydroxide, li) 2 CO 3 Li (lithium ion battery) 3 PO 4 The total amount of (2) was 0.74 wt%, and the mixture was kept at 870℃for 10 hours to obtain NCM raw material powder 16. The powder had a volume-based D50 particle size of 7.4. Mu.m.
[ production of NCM raw material powder 17 ]
In a range of a molar ratio Li/(Ni+Co+Mn) of 1.15, a commercially available (Ni 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder (average particle diameter 9-10 μm) and Li 2 CO 3 Li is added to the powder (average particle diameter 3 μm) 3 PO 4 Powder (average particle diameter 0.5 μm) (relative to NCM hydroxide, li) 2 CO 3 Li (lithium ion battery) 3 PO 4 The total amount of (2) was 1.8% by weight, and the mixture was kept at 870℃for 10 hours to obtain NCM raw material powder 17. The powder had a volume-based D50 particle size of 7.5. Mu.m.
[ production of NCM raw material powder 18 ]
In a range of a molar ratio Li/(Ni+Co+Mn) of 1.15, a commercially available (Ni 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder (average particle diameter 9-10 μm) and Li 2 CO 3 Li is added to the powder (average particle diameter 3 μm) 3 PO 4 Powder (average particle diameter 0.5 μm) (relative to NCM hydroxide, li) 2 CO 3 Li (lithium ion battery) 3 PO 4 The total amount of (2) was 3.6% by weight, and the mixture was kept at 870℃for 10 hours to obtain NCM raw material powder 18. The powder had a volume-based D50 particle size of 7.7. Mu.m.
[ production of NCM raw material powder 19 ]
Commercially available (Ni) was weighed so that the molar ratio of Li/(Ni+Co+Mn) was 1.15 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder (average particle diameter 9-10 μm) and Li 2 CO 3 After mixing the powders (average particle diameter: 3 μm), they were kept at 750℃for 10 hours to obtain NCM raw material powder 19. The powder had a volume-based D50 particle size of 7.0. Mu.m.
[ production of NCM raw material powder 20 ]
Adding Li to NCM raw powder 19 3 BO 3 (relative to NCM raw material powder 19 and Li 3 BO 3 Is 9.2 wt%, li 3 PO 4 (relative to NCM raw material powder 19 and Li 3 PO 4 The total amount of (2) was 1.0 wt%, wet-grinding by a ball mill, and mixing the resultant with a solidThe product standard D50 particle size was adjusted to about 0.5. Mu.m, and then dried to obtain NCM raw material powder 20.
[ production of NCM raw material powder 21 ]
Adding Li to NCM raw powder 19 3 BO 3 (relative to NCM raw material powder 19 and Li 3 BO 3 Is 9.2 wt%, li 3 PO 4 (relative to NCM raw material powder 19 and Li 3 PO 4 The total amount of (2) was 2.5% by weight, and the NCM raw material powder 21 was obtained by wet grinding with a ball mill, adjusting the volume-based D50 particle diameter to about 0.5 μm, and then drying.
[ production of NCM raw material powder 22 ]
Adding Li to NCM raw powder 19 3 BO 3 (relative to NCM raw material powder 19 and Li 3 BO 3 Is 9.2 wt%, li 3 PO 4 (relative to NCM raw material powder 19 and Li 3 PO 4 The total amount of (a) was 5.0 wt.%, and the NCM raw material powder 22 was obtained by wet grinding with a ball mill, adjusting the volume-based D50 particle diameter to about 0.5 μm, and then drying.
Using the above raw material powders 1 to 22, positive electrode plates and batteries were produced as described below, and various evaluations were performed.
Example 1
(1) Manufacture of positive plate
(1a) Manufacture of NCM Green sheet
First, as shown in tables 1A to 1C, NCM raw material powders 1 and 2 were prepared in an amount of 80:20 (weight ratio) were uniformly mixed to prepare an NCM mixed powder a. The mixed powder a, a solvent for casting, a binder, a plasticizer and a dispersant are mixed. After the viscosity of the obtained paste was adjusted, the paste was molded into a sheet on a PET (polyethylene terephthalate) film, thereby producing an NCM green sheet. The thickness of the NCM green sheet was adjusted to be 100 μm after firing.
(1b) Manufacture of NCM sintered plate
NCM green sheets peeled from PET film were punched into a circular shape having a diameter of 11mm by a punch, and placed in a firing sagger. Firing was performed by heating to 940℃at a heating rate of 200℃per hour and holding for 10 hours. The thickness of the obtained sintered plate was about 100 μm by SEM observation. An Au film (thickness 100 nm) was formed as a collector layer on one side of the NCM sintered plate by sputtering. Thus, a positive electrode plate was obtained.
(2) Production of negative electrode plate
(2a) LTO green sheet production
Commercially available TiO to be weighed in such a way that the molar ratio Li/Ti is 0.84 2 Powder (average particle diameter 1 μm or less) and Li 2 CO 3 After mixing the powders (average particle diameter 3 μm), the mixture was kept at 1000℃for 2 hours to obtain a powder composed of LTO particles. The powder was subjected to wet pulverization by a ball mill to an average particle size of about 2 μm, and then mixed with a solvent, a binder, a plasticizer and a dispersing agent for casting. After the viscosity of the obtained paste was adjusted, the paste was molded into a sheet on a PET film, thereby producing an LTO green sheet. The thickness of the LTO green sheet was adjusted to be 130 μm after firing.
(2b) LTO sintered plate production
LTO green sheets peeled from PET film were punched into a circular shape having a diameter of 11mm by a punch, and placed in a firing sagger. The temperature was raised to 850℃at a heating rate of 200℃per hour, and the mixture was kept for 2 hours, whereby firing was performed. The thickness of the obtained sintered plate was found to be about 130 μm by SEM observation. An Au film (thickness 100 nm) was formed as a collector layer on one side of the LTO sintered plate by sputtering. Thus, a negative electrode plate was obtained.
(3) Fabrication of solid electrolyte
(3a) Preparation of raw material mixed powder
Li is mixed with 2 SO 4 Powder (commercial product, purity 99% or more), liOH powder (commercial product, purity 98% or more), and Li 3 BO 3 (commercially available product with purity of 99% or more) according to Li 2 SO 4 ：LiOH：Li 3 BO 3 =1: 2.6:0.05 (molar ratio) to obtain a raw material mixed powder. These powders were handled in a glove box in an Ar atmosphere with sufficient attention so as not to undergo deterioration such as moisture absorption.
(3b) Melt synthesis
The raw material mixed powder was placed in a crucible made of high purity alumina in an Ar atmosphere. The crucible was fixed to an electric furnace, and heat-treated at 430℃in an Ar atmosphere for 2 hours to prepare a melt. Next, the melt was cooled at 100 ℃/h in an electric furnace to form a solidification.
(3c) Mortar crushing
The obtained coagulum was pulverized in a glove box in an Ar atmosphere using a mortar, whereby a solid electrolyte powder having a volume-based D50 particle diameter of 5 to 50 μm was obtained.
(4) Fabrication of all-solid-state battery
A solid electrolyte powder is placed on the positive electrode plate, and a negative electrode plate is placed on the solid electrolyte powder. Further, a heavy object was placed on the negative plate, and heated at 400℃for 45 minutes in an electric furnace. At this time, the solid electrolyte powder is melted and solidified, and a solid electrolyte layer is formed between the electrode plates. A battery was fabricated using the obtained single cell composed of positive electrode plate/solid electrolyte/negative electrode plate.
(5) Evaluation
(5a) Degree of orientation
XRD (X-ray diffraction) measurement was performed on the positive electrode plate produced in the above (1). The measurement was performed as follows: XRD curve was measured when the plate surface of the positive electrode plate was irradiated with X-rays using an XRD apparatus (D8 ADVANCE, manufactured by BRUKER Co.). From the XRD curve, the diffraction intensity (peak height) I of NCM derived from the (003) plane was calculated [003] Relative to the diffraction intensity (peak height) I originating from the (104) plane [104] The ratio of (I) is I [003] /I [104] This was set as the degree of orientation.
(5b) Measurement of thickness and porosity
The thickness and porosity (vol%) of each of the positive electrode plate (NCM sintered plate in a state free from solid electrolyte) produced in the above (1) and the negative electrode plate (LTO sintered plate in a state free from solid electrolyte) produced in the above (2) were measured as follows. First, after resin filling is performed on the positive electrode plate (or negative electrode plate), cross-sectional polishing is performed by ion milling, and then, the polished cross-section is observed by SEM, and a cross-sectional SEM image is obtained. From this SEM image, the thickness was calculated. The SEM image of the porosimetry was an image at 1000 times and 500 times magnification. The obtained Image was subjected to 2-valued processing using Image analysis software (Image-Pro Premier, manufactured by Media Cybernetics corporation), and the ratio (%) of the area of the resin-filled portion in the positive electrode plate (or negative electrode plate) to the total area of the portion of the positive electrode active material (or negative electrode active material) and the portion (originally the portion of the air hole) was calculated and was defined as the porosity (%) of the positive electrode plate (or negative electrode plate). The threshold value for the 2-valued calculation was set by using 2-valued calculation of oxford as a discriminant analysis method. The porosity of the positive electrode plate is 38% (i.e., density 62%) as shown in table 2.
(5c) Determination of average gas pore size
The average pore diameter was measured as follows using the SEM image for porosimetry described above. The positive electrode active material (or negative electrode active material) in the positive electrode plate (or negative electrode plate) and the resin-filled portion (originally the air hole portion) were separated by performing a 2-valued process using Image analysis software (manufactured by Media Cybernetics corporation). Then, the maximum martin diameter of each region was obtained in the region of the resin-filled portion, and the average value of the diameters was defined as the average pore diameter (μm) of the positive electrode plate (or negative electrode plate). The average gas pore diameter of the positive electrode plate is shown in Table 2, and the average gas pore diameter of the negative electrode plate is 2.1. Mu.m.
(5d) Every 1 μm 2 Measurement of interfacial length per Cross-sectional area
Using the SEM image for porosimetry described above, each 1 μm was measured as follows 2 Interfacial length per unit cross-sectional area. The positive electrode active material in the positive electrode plate and the resin-filled portion (the portion that was originally air-porous) were separated by performing a 2-valued processing using Image analysis software (manufactured by Media Cybernetics). Then, in the region of the resin-filled portion, the perimeter of the entire region (i.e., the total length of the interface between the portion of the positive electrode active material and the resin-filled portion) and the analyzed entire region (i.e., the portion including the positive electrode active material and the resin-filled portion) were obtained Areas of both). The circumferential length divided by the area of the entire region analyzed was set to 1 μm 2 Interfacial length (μm) per unit cross-sectional area. The results are shown in Table 2.
(5e) Determination of molar ratio of metallic element in positive plate
The molar ratio Li/(Ni+Co+Mn) of the Li content in the positive electrode plate produced in (1) above to the total content of Ni, co and Mn was calculated from the measurement result of the metal element analysis by inductively coupled plasma emission spectrometry (ICP-AES method). The results are shown in Table 2.
(5f) Identification of solid electrolytes by XRD
The LiOH-Li obtained in the above (3 c) was subjected to X-ray diffraction (XRD) 2 SO 4 The solid electrolyte was analyzed, and as a result, it was identified as 3 LiOH. Li 2 SO 4 。
(5g) Evaluation of charge and discharge (cycle maintenance)
The discharge capacity of the battery produced in the above (4) was measured at an operating temperature of 150℃in a voltage range of 2.5V to 1.5V. The measurement was performed by performing constant-current and constant-voltage charging until the battery voltage reached the upper limit of the voltage range, and then discharging until the battery voltage reached the lower limit of the voltage range. This test (cycle test) was repeated to calculate a maintenance rate of discharge capacity at a predetermined cycle (=100× (discharge capacity at a predetermined cycle)/(initial discharge capacity)). The results are shown in Table 2.
Example 2
In the production of the positive electrode plate of (1), 1) the following steps are used as 90:10 (weight ratio) comprises NCM mixed powder B of NCM raw material powders 1 and 3 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was set to 950 ℃.
Example 3
In the production of the positive electrode plate of (1), 1) only NCM raw material powder 5 shown in tables 1A to 1C was used instead of mixed powder a; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃. The battery fabricated in this example was disassembled in a glove box, and electron microscopic observation and element mapping using an Electron Probe Microanalyzer (EPMA) were performed on the interface between the positive electrode plate and the solid electrolyte. Fig. 1 shows an electron micrograph and an EPMA map image of a cross section of a positive electrode active material (NCM)/solid electrolyte of an all-solid battery fabricated in this example. The leftmost image in fig. 1 is an electron micrograph (white portion corresponds to NCM and black portion corresponds to solid electrolyte), and from this point on, the EPMA map images of Mn, co, and Ni are shown in order to the right.
Example 4
In the production of the positive electrode plate of (1), 1) only NCM raw material powder 6 shown in tables 1A to 1C was used instead of mixed powder a; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 5
In the production of the positive electrode plate of (1), 1) the following steps are used as 90:10 (weight ratio) comprises NCM mixed powder C of NCM raw material powders 7 and 8 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 6
In the production of the positive electrode plate of (1), 1) a positive electrode plate of 95:5 (weight ratio) comprises NCM mixed powder D of NCM raw material powders 7 and 8 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was set to 950 ℃.
Example 7
In the production of the positive electrode plate of (1), 1) a positive electrode plate of 95:5 (weight ratio) comprises NCM mixed powder E of NCM raw material powders 7 and 9 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 8
In the production of the positive electrode plate of (1), 1) a positive electrode plate of 95:5 (weight ratio) comprises NCM mixed powder F of NCM raw material powders 7 and 10 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃. Fig. 3 shows an electron micrograph (reflected electron image) of a cross section of the positive electrode plate produced in this example.
Example 9
In the production of the positive electrode plate of (1), 1) a positive electrode plate of 95:5 (weight ratio) comprises NCM mixed powder G of NCM raw material powders 7 and 11 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 10
In the production of the positive electrode plate of (1), 1) a positive electrode plate of 95:5 (weight ratio) comprises NCM mixed powder H of NCM raw material powders 7 and 12 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 11
In the production of the positive electrode plate of (1), 1) the following steps are used as 90:10 (weight ratio) comprises NCM mixed powder I of NCM raw material powders 16 and 20 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 12
In the production of the positive electrode plate of (1), 1) the following steps are used as 90:10 (weight ratio) comprises NCM mixed powder J of NCM raw material powders 17 and 21 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃. Fig. 4 shows an electron micrograph (reflected electron image) of a cross section of the positive electrode plate after resin filling of the positive electrode plate manufactured in this example.
Example 13
In the production of the positive electrode plate of (1), 1) the following steps are used as 90:10 (weight ratio) comprises NCM mixed powder K of NCM raw material powders 18 and 22 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 14(comparison)
In the production of the positive electrode plate of (1), 1) only NCM raw material powder 4 shown in tables 1A to 1C was used instead of mixed powder a; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃. The battery fabricated in this example was disassembled in a glove box, and electron microscopic observation and element mapping using an Electron Probe Microanalyzer (EPMA) were performed on the interface between the positive electrode plate and the solid electrolyte. Fig. 2 shows an electron micrograph and an EPMA map image of a cross section of a positive electrode active material (NCM)/solid electrolyte of the all-solid battery fabricated in this example. The leftmost image in fig. 2 is an electron micrograph (white portion corresponds to NCM and black portion corresponds to solid electrolyte), and from this point on, the EPMA map images of Mn, co, and Ni are shown in order to the right.
Example 15(comparison)
In the production of the positive electrode plate of (1), 1) only the NCM raw material powder 14 shown in tables 1A to 1C was used instead of the mixed powder a; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was 920 ℃.
Example 16(comparison)
In the production of the positive electrode plate of (1), 1) only the NCM raw material powder 15 shown in tables 1A to 1C was used instead of the mixed powder a; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was set to 890 ℃.
Example 17(comparison)
In the production of the positive electrode plate of (1), 1) the following steps are used as 90:10 (weight ratio) comprises NCM mixed powder L of NCM raw material powders 7 and 13 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was set to 950 ℃.
Example 18(comparison)
In the production of the positive electrode plate of (1), 1) a positive electrode plate of 95:5 (weight ratio) comprises NCM mixed powder M of NCM raw material powders 7 and 13 shown in tables 1A to 1C instead of mixed powder A; 2) A positive electrode plate and a battery were produced in the same manner as in example 1 except that the firing temperature was set to 950 ℃.
Results
Table 2 shows the specifications of the positive electrode plates and the evaluation results of the single cells produced in each example. The charge and discharge characteristics were compared with the same number of cycles at the same rate, and the maintenance rate of the discharge capacity at the predetermined cycle (=100× (discharge capacity at the predetermined cycle)/(initial discharge capacity)) was calculated, and is shown in table 2. In each example, the LiOH-Li was subjected to X-ray diffraction (XRD) 2 SO 4 The solid electrolyte was analyzed, and as a result, it was identified as 3 LiOH. Li 2 SO 4 。
[ Table 1A ]
[ Table 1B ]
[ Table 1C ]
TABLE 2
From SEM observation and element mapping using EPMA (fig. 1 and 2), it can be confirmed that: is added with additive (Li) 3 PO 4 ) Is described in (example 3; referring to FIG. 1) and no Li addition 3 PO 4 Compared with pure NCM (example 14 (comparative); see FIG. 2) containing such an additive, diffusion of the transition metal into the solid electrolyte portion in the voids of the positive electrode plate is suppressed. This is considered as follows: adopts the additive Li 3 PO 4 In the positive electrode plates (examples 3, 4 and 11 to 13) of NCM, the decrease in Li ion conductivity due to the deterioration of the solid electrolyte was alleviated, and as a result, the cycle maintenance rate was improved. In addition, li is added with 3 BO 3 Or Li (lithium) 2 SO 4 The NCM (examples 1, 2 and 5 to 10) was considered to have an improved cycle retention rate as compared with the pure NCM: li (Li) 3 BO 3 Or Li (lithium) 2 SO 4 Is added with Li 3 PO 4 The same effect is obtained by adding (a) to the solution.
From fig. 3 showing an SEM image (reflected electron image) of the cross section of the positive electrode plate obtained in example 8, it can be confirmed that: other elements than Ni, co, and Mn are present in the NCM bulk. That is, since fig. 3 shows a darker color than the NCM part, this element is considered to be B (boron), which is an element lighter than Ni, co, and Mn. The B is considered to exist in the grain boundary.
From fig. 4 showing an SEM image (reflected electron image) of a cross section of the resin-filled positive electrode plate obtained in example 12, it can be confirmed that: the other elements are present so as to cover the air hole portion of the sintered plate. In the SEM image, it is considered that 3 color regions are observed: the brightest colored portion is NCM, the darkest colored portion is resin (C: carbon), and the intermediate colored portions are portions containing other elements present on the surface of NCM. The intermediate color portion is darker than NCM and lighter than resin, and is considered to contain B (boron) and P (phosphorus) contained in the additive. The above B and P are thought to precipitate on the NCM surface.
The batteries of examples 1 to 13 using the positive electrode active material satisfying the requirements of the present invention exhibited significantly higher cycle retention rates than the batteries of examples 14 to 18 (comparative examples) not satisfying the requirements of the present invention. This is thought to be because: li precipitated on a part of the surface of the lithium composite oxide 3 BO 3 、Li 3 PO 4 And/or Li 2 SO 4 Side reactions of lithium composite oxide and solid electrolyte are suppressed, and Li precipitated at a part of grain boundary 3 BO 3 、Li 3 PO 4 And/or Li 2 SO 4 The stress of expansion and contraction of the positive electrode active material is relaxed. Consider that: accordingly, the phenomena of a decrease in Li ion conductivity due to degradation of the solid electrolyte, formation of a high-resistance layer that inhibits Li ion conduction at the interface between the positive electrode layer and the solid electrolyte, and an increase in diffusion resistance between the positive electrode active materials are alleviated, and the cycle maintenance rate is improved.
< examples 19 to 33 >
The examples described below are examples related to all-solid secondary batteries in which the positive electrode and the negative electrode are in the form of a mixture.
Example 19
(1) Preparation of positive electrode active material powder
Commercially available (Ni) was weighed so that the molar ratio of Li/(Ni+Co+Mn) was 1.07 0.3 Co 0.6 Mn 0.1 )(OH) 2 Powder (average particle diameter 9-10 μm) and Li 2 CO 3 After mixing the powders (average particle diameter: 3 μm), they were kept at 950℃for 10 hours to obtain NCM raw material powder 23. Li is added to the obtained NCM raw material powder 23 3 BO 3 (relative to NCM raw material powder 23 and Li 3 BO 3 In terms of the total amount of (2), 1.0 wt.%, li 3 PO 4 (relative to NCM raw material powder 23 and Li 3 PO 4 The total amount of (2) was 1.0% by weight, and the mixture was kept at 950℃for 10 hours to obtain NCM powder.
(2) Preparation of negative electrode active material powder
Commercially available carbon powder (average particle diameter 10 to 14 μm) was prepared.
(3) Fabrication of solid electrolyte
(3a) Preparation of raw material powder
Li is mixed with 2 SO 4 Powder (commercial product, purity 99% or more), liOH powder (commercial product, purity 98% or more), and Li 3 BO 3 (commercially available product with purity of 99% or more) according to Li 2 SO 4 ：LiOH：Li 3 BO 3 =1: 2.2:0.05 (molar ratio) to obtain a raw material mixed powder. These powders were handled in a glove box in an Ar atmosphere with sufficient attention so as not to undergo deterioration such as moisture absorption.
(3b) Melt synthesis
The raw material mixed powder was put into a crucible of high purity alumina in an Ar atmosphere. The crucible was fixed to an electric furnace, and heat-treated at 430℃in an Ar atmosphere for 2 hours to prepare a melt. Next, the melt was cooled at 100 ℃/h in an electric furnace to form a solidification.
(3c) Crushing
The obtained coagulated material was pulverized in a glove box in an Ar atmosphere using a mortar, and further pulverized with a ball stone to obtain a solid electrolyte powder having an average particle diameter D50 of 1 to 20 μm.
(4) Fabrication of all-solid-state battery
(4a) Preparation of positive electrode mixture powder and negative electrode mixture powder
The positive electrode active material powder obtained in the above (1), the solid electrolyte powder obtained in the above (3), and an electron transfer auxiliary agent (acetylene black (commercially available product)) were mixed at a volume ratio of 60:40:2, and mixing them in a mortar to prepare a positive electrode mixture powder. Similarly, the negative electrode active material powder obtained in the above (2), the solid electrolyte powder obtained in the above (3), and the electron transfer auxiliary agent (acetylene black (commercially available product)) were mixed in a volume ratio of 60:40:2, and mixing them in a mortar to prepare a negative electrode mixture powder.
(4b) Compression molding
In a pressing mold having a pore diameter of 10mm, powders were placed in layers so that the thicknesses of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer were 100 μm, 500 μm, and 110 μm, respectively, in this order, and the layers were pressed at 100 MPa. After 3 layers were laminated in this manner, the laminate was pressurized at 150MPa to obtain a pressed molded body.
(4c) Assembly of a pressing jig
The press-formed body was sandwiched between 1 pair of stainless steel plates in a layer configuration of stainless steel plates/positive electrode layer/solid electrolyte layer/negative electrode layer/stainless steel plates, and the press-formed body was held together with the stainless steel plates at 150MPa, to obtain an all-solid-state battery as a single cell for evaluation.
(5) Evaluation
(5a) Determination of molar ratio of metallic element in positive electrode layer
The molar ratio Li/(Ni+Co+Mn) of the Li content in the positive electrode layer prepared in (1) above to the total content of Ni, co and Mn was calculated from the measurement result of the metal element analysis by inductively coupled plasma emission spectrometry (ICP-AES method). The results are shown in Table 3.
(5b) Identification of solid electrolytes by XRD
The LiOH-Li obtained in the above (3 c) was subjected to X-ray diffraction (XRD) 2 SO 4 The solid electrolyte was analyzed, and as a result, it was identified as 3 LiOH. Li 2 SO 4 。
(5c) Evaluation of charge and discharge (cycle maintenance)
The discharge capacity of the battery produced in the above (4) was measured at an operating temperature of 150℃in a voltage range of 4.15V to 2.0V. The measurement was performed by performing constant-current and constant-voltage charging until the battery voltage reached the upper limit of the voltage range, and then discharging until the battery voltage reached the lower limit of the voltage range. This test (cycle test) was repeated to calculate a maintenance rate of discharge capacity at a predetermined cycle (=100× (discharge capacity at a predetermined cycle)/(initial discharge capacity)). The results are shown in Table 3.
(5d) Measurement of filling Rate
The filling ratio (vol%) of each active material of the positive electrode and the negative electrode of the all-solid-state battery produced in the above (4) was measured as follows. First, after the all-solid-state battery was subjected to cross-sectional milling by ion milling, the cross-section of the milled positive electrode (or negative electrode) was observed by SEM, and a cross-sectional SEM image was obtained. The SEM image was set to an image at 1000 times magnification. The obtained Image was subjected to 2-valued processing using Image analysis software (Image-Pro Premier, manufactured by Media Cybernetics). The threshold value at the time of 2-valued was set by using 2-valued of oxford as a discriminant analysis method. Based on the obtained 2-valued image, the filling rate F (%) of the positive electrode active material (or negative electrode active material) in the positive electrode (or negative electrode) was calculated by the following formula. The results are shown in Table 3.
Filling rate f= [ S ] A /(S A +S B )]×100
(wherein S A To 2-value the area of the portion occupied by the positive electrode active material (or negative electrode active material) in the image, S B To 2-value the area of the portion of the image other than the positive electrode active material (or negative electrode active material) and including the area occupied by the solid electrolyte, the electron conduction auxiliary agent, and the void
Example 20
The production of the negative electrode active material powder was performed as follows, and the production and evaluation of the battery were performed in the same manner as in example 19 except that the discharge capacity of the battery at an operating temperature of 150 ℃ was measured in the voltage range of 2.7V to 1.5V in the charge-discharge evaluation of (5 c) above.
(preparation of negative electrode active material powder)
Commercially available TiO to be weighed in such a way that the molar ratio Li/Ti is 0.84 2 Powder (average particle diameter 1 μm or less) and Li 2 CO 3 After mixing the powders (average particle size 3 μm), the mixture was kept at 1000℃for 2 hours, to obtain a powder having an average particle size of about 3.5 μm composed of LTO particles.
Example 21
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 3 BO 3 (relative to NCM raw material powder 23 and Li 3 BO 3 In terms of the total amount of (2), 1.0 wt.%, li 3 PO 4 (relative to NCM raw material powder 23 and Li 3 PO 4 A battery was produced and evaluated in the same manner as in example 19, except that the total amount of (a) was 2.5% by weight, and the mixture was kept at 950 ℃ for 10 hours to obtain NCM powder.
Example 22
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 3 BO 3 (relative to NCM raw material powder 23 and Li 3 BO 3 In terms of the total amount of (2), 1.0 wt.%, li 3 PO 4 (relative to NCM raw material powder 23 and Li 3 PO 4 A battery was produced and evaluated in the same manner as in example 19, except that the total amount of (a) was 5.0% by weight, and the mixture was kept at 950 ℃ for 10 hours to obtain NCM powder.
Example 23
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 3 PO 4 (relative to NCM raw material powder 23 and Li 3 PO 4 A battery was produced and evaluated in the same manner as in example 19, except that the total amount of (a) was 1.0% by weight, and the mixture was kept at 950 ℃ for 10 hours to obtain NCM powder.
EXAMPLE 24
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 3 PO 4 (relative to NCM raw material powder 23 and Li 3 PO 4 A battery was produced and evaluated in the same manner as in example 19, except that the total amount of (a) was 5.0% by weight, and the mixture was kept at 950 ℃ for 10 hours to obtain NCM powder.
Example 25
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 2 SO 4 (relative to NCM raw material powder 23 and Li 2 SO 4 The procedure of example 19 was repeated except that the total amount of (2) was 1.0% by weight, and the mixture was kept at 950℃for 10 hours to obtain NCM powderAnd (5) manufacturing and evaluating the battery.
Example 26
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 2 SO 4 (relative to NCM raw material powder 23 and Li 2 SO 4 A battery was produced and evaluated in the same manner as in example 19, except that the total amount of (a) was 5.0% by weight, and the mixture was kept at 950 ℃ for 10 hours to obtain NCM powder.
Example 27
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 3 BO 3 (relative to NCM raw material powder 23 and Li 3 BO 3 A battery was produced and evaluated in the same manner as in example 19, except that the total amount of (a) was 1.0% by weight, and the mixture was kept at 950 ℃ for 10 hours to obtain NCM powder.
EXAMPLE 28
In the production of the positive electrode active material powder of the above (1), li is added to the NCM raw material powder 23 3 BO 3 (relative to NCM raw material powder 23 and Li 3 BO 3 A battery was produced and evaluated in the same manner as in example 19, except that the total amount of (a) was 5.0% by weight, and the mixture was kept at 950 ℃ for 10 hours to obtain NCM powder.
Example 29
A battery was produced and evaluated in the same manner as in example 19, except that the positive electrode active material powder was produced as follows.
(1') preparation of Positive electrode active material powder
Commercially available (Ni) was weighed so that the molar ratio of Li/(Ni+Co+Mn) was 1.05 0.5 Co 0.2 Mn 0.3 )(OH) 2 Powder (average particle diameter 9 μm) and Li 2 CO 3 After mixing the powders (average particle diameter: 3 μm), they were kept at 920℃for 10 hours to obtain NCM raw material powder 24. Li is added to the obtained NCM raw material powder 24 3 BO 3 (relative to NCM raw material powder 24 and Li) 3 BO 3 In terms of the total amount of (2), 1.0 wt.%, li 3 PO 4 (relative to NCM raw material powder 24 and Li) 3 PO 4 The total amount of (2) was 1.0% by weight, and the mixture was kept at 920℃for 10 hours to obtain NCM powder.
Example 30
In the production of the positive electrode active material powder of the above (1'), li is added to the NCM raw material powder 24 3 PO 4 (relative to NCM raw material powder 24 and Li) 3 PO 4 A battery was produced and evaluated in the same manner as in example 29, except that the total amount of (a) was 1.0% by weight, and the mixture was kept at 920 ℃ for 10 hours to obtain NCM powder.
Example 31(comparison)
In the production of the positive electrode active material powder of the above (1), li is not carried out 3 BO 3 Li (lithium ion battery) 3 PO 4 A battery was produced and evaluated in the same manner as in example 19, except that the NCM raw material powder 23 was directly used as the positive electrode active material powder.
Example 32(comparison)
In the production of the positive electrode active material powder of the above (1), li is not carried out 3 BO 3 Li (lithium ion battery) 3 PO 4 A battery was produced and evaluated in the same manner as in example 20, except that the NCM raw material powder 23 was directly used as the positive electrode active material powder, followed by the heat treatment.
Example 33(comparison)
In the production of the positive electrode active material powder of the above (1'), li is not carried out 3 BO 3 Li (lithium ion battery) 3 PO 4 A battery was produced and evaluated in the same manner as in example 29, except that the NCM raw material powder 24 was directly used as the positive electrode active material powder, followed by the heat treatment.
Results
Table 3 shows the specifications of the mixture cells and the evaluation results of the cells produced in each example. The charge and discharge characteristics are the same at the same rateThe cycle numbers were compared, and the maintenance rate of discharge capacity at the time of a predetermined cycle (=100× (discharge capacity at the time of a predetermined cycle)/(initial discharge capacity)) was calculated and shown in table 3. In each example, the LiOH-Li was subjected to X-ray diffraction (XRD) 2 SO 4 The solid electrolyte was analyzed, and as a result, it was identified as 3 LiOH. Li 2 SO 4 。
TABLE 3
In the all-solid secondary battery in which the positive electrode and the negative electrode were in the form of a mixture, similarly, the batteries of examples 19 to 30 using the positive electrode active material satisfying the requirements of the present invention exhibited significantly high cycle maintenance rates as compared with the batteries of examples 31 to 33 (comparative examples) not satisfying the requirements of the present invention. Li deposited on a part of the surface of a lithium composite oxide, which can be confirmed in an all-solid secondary battery in which the positive electrode and the negative electrode are in the form of sintered plates 3 BO 3 、Li 3 PO 4 And/or Li 2 SO 4 Side reactions of lithium composite oxide and solid electrolyte are suppressed, and Li precipitated at a part of grain boundary 3 BO 3 、Li 3 PO 4 And/or Li 2 SO 4 Since stress and the like that alleviate expansion and contraction of the positive electrode active material similarly occur in the battery in the form of a mixture, it is considered that the cycle maintenance rate is improved.
Claims (16)
1. A positive electrode active material for a lithium ion secondary battery,
the positive electrode active material is characterized in that,
the positive electrode active material contains a lithium composite oxide having a layered rock salt structure and containing Li, ni, co and Mn, and further contains a material selected from the group consisting of Li 3 BO 3 、Li 3 PO 4 Li (lithium ion battery) 2 SO 4 At least 1 additive of (a) in the composition.
2. The positive electrode active material according to claim 1, wherein,
the additive is present in a state of being precipitated in at least a part of the grain boundary and the surface of the lithium composite oxide.
3. The positive electrode active material according to claim 1 or 2, wherein,
the content of the additive is 0.1 to 10% by weight relative to the total content of the lithium composite oxide and the additive.
4. The positive electrode active material according to any one of claim 1 to 3, wherein,
the positive electrode active material is in the form of a sintered plate.
5. The positive electrode active material according to claim 4, wherein,
degree of orientation I of the sintered plate [003] /I [104] 1.2 to 3.6, the degree of orientation I [003] /I [104] The definition is as follows: diffraction intensity I from the (003) plane in XRD curve measured by X-ray diffraction, XRD [003] Relative to the diffraction intensity I originating from the (104) plane [104] Is a ratio of (2).
6. The positive electrode active material according to any one of claim 4 or 5, wherein,
every 1 μm of the sintered plate 2 The interface length per unit cross-sectional area is 0.45 μm or less.
7. The positive electrode active material according to any one of claims 4 to 6, wherein,
the porosity of the sintered plate is 20-40%.
8. The positive electrode active material according to any one of claims 4 to 7, wherein,
the average pore diameter of the sintered plate is 3.5 μm or more.
9. The positive electrode active material according to any one of claim 4 to 8, wherein,
the thickness of the sintered plate is 30-300 mu m.
10. The positive electrode active material according to any one of claim 1 to 3, wherein,
the positive electrode active material is in the form of powder.
11. The positive electrode active material according to any one of claims 1 to 10, wherein,
The molar ratio of Li/(Ni+Co+Mn) in the positive electrode active material is 0.95-1.10.
12. A lithium ion secondary battery, characterized by comprising:
a positive electrode layer containing the positive electrode active material according to any one of claims 1 to 11;
a negative electrode layer containing a negative electrode active material; and
LiOH·Li 2 SO 4 a solid electrolyte of LiOH.Li 2 SO 4 A solid electrolyte is interposed between the positive electrode layer and the negative electrode layer.
13. The lithium ion secondary battery according to claim 12, wherein,
the positive electrode active material is in the form of a sintered plate.
14. The lithium ion secondary battery according to claim 12, wherein,
the positive electrode layer contains particles of the positive electrode active material and the LiOH-Li in the form of a mixture 2 SO 4 Particles of a solid electrolyte and an electron conduction auxiliary agent.
15. The lithium-ion secondary battery according to any one of claims 12 to 14, wherein,
the negative electrode active material is Li 4 Ti 5 O 12 。
16. The lithium-ion secondary battery according to any one of claims 12 to 15, wherein,
the LiOH-Li 2 SO 4 The solid electrolyte contains 3LiOH Li identified by X-ray diffraction 2 SO 4 Is a solid electrolyte of (a).
Applications Claiming Priority (5)
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| JPPCT/JP2020/048035 | 2020-12-22 | ||
| PCT/JP2020/048035 WO2022137360A1 (en) | 2020-12-22 | 2020-12-22 | Lithium composite oxide sintered plate and all-solid-state secondary battery |
| JPPCT/JP2021/013156 | 2021-03-26 | ||
| PCT/JP2021/013156 WO2022137583A1 (en) | 2020-12-22 | 2021-03-26 | Positive electrode active material and lithium-ion secondary battery |
| PCT/JP2021/045009 WO2022138148A1 (en) | 2020-12-22 | 2021-12-07 | Positive electrode active material and lithium-ion secondary battery |
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| JP5601157B2 (en) * | 2010-11-01 | 2014-10-08 | トヨタ自動車株式会社 | Positive electrode active material, positive electrode active material layer, all-solid battery, and method for producing positive electrode active material |
| JP6433086B2 (en) | 2014-03-31 | 2018-12-05 | 日本碍子株式会社 | All solid lithium battery |
| JP6910595B2 (en) * | 2017-06-05 | 2021-07-28 | 株式会社Ｇｓユアサ | Non-aqueous electrolyte secondary battery |
| JP6956801B2 (en) | 2017-11-10 | 2021-11-02 | 日本碍子株式会社 | All-solid-state lithium battery and its manufacturing method |
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| TWI785239B (en) * | 2018-05-17 | 2022-12-01 | 日商日本碍子股份有限公司 | lithium secondary battery |
| JP6780140B1 (en) * | 2020-01-17 | 2020-11-04 | 住友化学株式会社 | Mixed powder for all-solid-state lithium-ion batteries, mixed paste for all-solid-state lithium-ion batteries, electrodes and all-solid-state lithium-ion batteries |
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| EP4270546A1 (en) | 2023-11-01 |
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